Control devices of a hydrostatic transmission

ABSTRACT

The invention refers to control devices applied in a hydrostatic transmission, which includes a motor pump MP, a hydrostatic circuit HC  1  and HC  2  and an impelling pump IP, which is formed by a rotor  1 , a stator  2  and a body  3 ; the fluid debit is infinitely variable and is obtained by the radial and variable decentralisation of the said stator  2 , by means of the impulsion of the rods A and B. 
     The devices are constituted by pistons  4  and  5 , which impel the rods A and B, and are inserted in cylinders  6  and  7 ; by springs systems  9, 10  and  11 , which regulate the position of the pistons and of the rods, and by a command formed by a valve  8 , inserted in a vacuum circuit with ways V 1  and V 2 , which communicate with the cylinder  7.    
     Through way V 1  the vacuum effect acts on the piston  5 , obtaining the decentralisation of the stator  2  in direction of the rod A; the fluid pressure transmitted by the extension HE to the piston  4 , regulates the debit of the impelling pump and the rotation speed of the motor pump, whose rotation direction is the same as the impelling pump, FIG.  1.    
     Through way V 2  the decentralisation of the stator  2  is obtained in the inverse direction to the rod A, and the rotation direction of the motor pump is inverse of the rotation direction of the impelling pump, FIG.  2.    
     When the command is not activated, no fluid impulsion is transmitted by the impelling pump and there is no rotation of the motor pump, FIG.  3.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention simplifies and renders practical the control ofhydrostatic transmissions in which the pumps, with either impelling ormotor functions, are preferably of the rotational type and of infinitelyvariable debit of fluid, so that the variation of the said debit may beautomatic, according to the variation of the pressure in the fluidcircuit of the transmission. The said pumps have an internal stator 2,which is decentralised in axial way, between the rotor 1 and the box orexternal stator 3 by means of the rods A and B.

A fundamental characteristic of the said pumps is the fact that thevariable work pressures of the fluid, which act on the internal side ofthe stator 2, are compensated and balanced on the corresponding externalside by equal fluid pressures.

2. Description of the Related Art

In the previous hydrostatic transmissions of the rotational type and ofvariable debit, a great obstacle has been the great strength that isnecessary to be applied in the impulsion of the internal stator in orderto be obtained the variation of the amplitude and direction of itsdecentralisation.

The said impulsion is opposed by the work pressures of the fluid, whichare produced in the internal side of the stator and which are opposed tothe said variation due to the fact that they are not balanced by equalpressures on the external and opposed side.

As a consequence, it is necessary to have impulsion systems based on“screw systems” or based on the hydrostatic systems of a great strengthand of a very complicated construction.

In short, there are several negative facts in the previous types ofhydrostatic transmissions:—lack of compensation and balance of the workpressures between the internal and the external sides of the movablestator;—excessive number of devices with heavy weight and highobstruction;—complicated and slow control;—the variation of the fluiddebit does not automatically respond to the pressure variation generatedin the proper transmission circuit, resulting from the variation of itswork load.

These negative facts have been preventing its application in numerouswork situations for hydrostatic transmissions.

For instance, in the hydrostatic transmission type described in theDocument U.S. Pat. No. 3,354,637 A (CROSWHITE), the movable stator isnot balanced in a hydrostatic way with the work forces of the fluid andits decentralisation can only be obtained by means of a strong system oflevers, resulting in an excessive and heavy obstruction.

The command system is a complication of hydrostatic valves which are intheir turn connected to a complication of hydrostatic cylinders of fluidsupply.

Besides, there is not a direct automatism between the variation of thefluid pressure in the main hydrostatic circuit, which results from thevariation of the work load and the debit variation of the said fluid.

This kind of hydrostatic transmission, which must be equipped withcomplicated and large performance and control devices and which do notpossess a direct automation, cannot have an easy practical application.

It is obvious that they do not have anything similar to thesimplification and lightness of the control devices and to the directautomatism, which are fundamental characteristics of the present and newinvention.

In the new invention, one piston only direct supplied by the fluidpressure of the proper transmission circuit and in co-operation with asimple system of laminar springs, performs automatically the variationof the stator decentralisation, which results in the direct obtaining ofthe variation of the fluid debit in correspondence with the variation ofthe work load of the transmission.

The considerations previously stated can be applicable in relation, tothe transmission type described in the Document U.S. Pat. No. 3,890,787A (VAUSON WARREN C) and in the following documents:

GB 992 587 A (VEB INDUSTRIEWERKE KARL-MARK-STADT:

U.S. Pat. No. 3,959,969 (TITTMANN EGON ET AL);

U.S. Pat. No. 3,808,814 A (MACY R).

SUMMARY OF THE INVENTION

The invention refers to control devices applied in a hydrostatictransmission, which includes a motor pump MP, a hydrostatic circuit HC 1and HC 2, and an impelling pump IP, which is formed by a rotor 1, astator 2 and a body 3; the fluid debit is infinitely variable and isobtained by the radial and variable decentralisation of the said stator2, by means of the impulsion of the rods A and B.

The devices are constituted by pistons 4 and 5, which impel the rods Aand B, and are inserted in cylinders 6 and 7; by springs systems 9, 10and 11, which regulate the position of the pistons and of the rods, andby a command formed by a valve 8, inserted in a vacuum circuit with waysV1 and V2, which communicate with the cylinder 7.

Through way V1 the vacuum effect acts on the piston 5, obtaining thedecentralisation of the stator 2 in direction of the rod A; the fluidpressure transmitted by the extension HE to the piston 4, regulates thedebit of the impelling pump and the rotation speed of the motor pump,whose rotation direction is the same as the impelling pump, FIG. 1.

Through way V2 the decentralisation of the stator 2 is obtained in theinverse direction to the rod A, and the rotation direction of the motorpump is inverse of the rotation direction of the impelling pump, FIG. 2.

When the command is not activated, no fluid impulsion is transmitted bythe impelling pump and there is no rotation of the motor pump, FIG. 3.

EXPLANATION OF THE INVENTION

Due to the fundamental characteristics of compensation and balance ofthe external and internal pressures to the movable stator 2, the basicpurposes of the invention are: to reduce the number of control devicesand to simplify their shape in order to obtain an insignificantobstruction; to optimize their functioning in order to obtain a directdecentralization variation of the stator and the corresponding automaticvariation of the fluid debit in correspondence with the variation ofwork load of the transmission.

In a previous application, we developed a hydrostatic pump IP, ofinfinitely variable debit, which includes a rotor 1, a stator 2 and abody 3; the infinitely variable debit is obtained by the radial andvariable decentralisation of the said stator by means of the impulsionof the rods, A and B.

The different work pressures of the fluid, which act on each internalside of the stator, are compensated and balanced on the correspondingexternal side by equal fluid pressures transmitted to chambers; each oneof the said chambers is contiguous to each one of the sides.

A great advantage of the application of this method is that the strengthapplied in the impulsion of the rods is small and independent from thework pressures of the fluid; this fact permits the application of theadequate devices, in order to obtain an easy and safe control of thevariation of the amplitude and of the direction of the decentralizationof the stator of a hydrostatic pump, either its function is impelling ormotor.

The said control devices of a hydrostatic transmission are constitutedby pistons 4 and 5, which give impulse to the rods A and B and areinserted in cylinders 6 and 7; by systems of springs 9, 10 and 11, whichregulate the position of the pistons and of the rods; and by atransmission control formed by a valve 8, inserted in a vacuum circuitwith two ways V1 and V2, which communicate with the second cylinder 7.

The application and the functioning of the said devices, are explainedbelow with the help of the description of three illustrative examples,and without a limited character, of the conception and application ofthe said devices, which perform the present invention in the preferredform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, represents in section the application of the control devices ina hydrostatic transmission, in which the decentralisation of the stator2 is obtained in the direction of the rod A; the motor pump MP has thesame direction of the rotation of the impelling pump IP.

FIG. 2, represents in section the application, in which thedecentralisation of the stator 2 is obtained in the inverse direction ofthe rod A; the rotation direction of the motor pump is inverse of theimpelling pump.

FIG. 3, represents in section the application, in which the stator is ina centralized position; no fluid impulsion is transmitted by theimpelling pump and there is no rotation of the motor pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Considering the application of the control devices in a hydrostatictransmission of infinitely variable speed, which includes an impellingpump as the one described above IP, associated with a motor pump MP bymeans of a fluid circuit HC 1 and HC 2, the said application isperformed as follows:

in the impelling pump IP, the piston 4 is inserted in the first cylinder6, it has a simple effect and impels the rod A through the top; itsretrocession is obtained by means of a system of springs 9; the saidcylinder communicates with the side HC 1 of the hydrostatic circuit ofthe transmission, by means of a hydrostatic extension HE;

the piston 5 is inserted in the second cylinder 7, it has a doubleeffect and is fastened with the rod B; its balance position is obtainedby the joint action of the springs systems 10 and 11, and its impulsionis regulated by the transmission command;

the regulation of the transmission command is obtained by the valve 8regulation directing, through ways V1 or V2, the activation of thevacuum effect to the second cylinder 7, in order to obtain the impulsionof the respective piston 5, in the direction of the decentralisation ofthe stator, determined by the said command.

DETAILED DESCRIPTION

FIGS. 1, 2 and 3 of the drawings, show the functioning of a hydrostatictransmission of infinitely variable speed, in which the control devicesare applied to an impelling pump IP of infinitely variable debit, as itwas described above.

In FIG. 1, the motor pump MP has the same rotation direction of theimpelling pump IP;

the transmission command directs the activation of the vacuum effectthrough way V1 to the second cylinder 7, in order to impel the piston 5and the rod B which is fastened to it, in the direction of the rod A; itis obtained the decentralization of the stator of the impelling pump IPin the direction of the said rod A;

agreeing that the rotor rotation of the impelling pump IP is in thedirection C, the fluid is impelled by the said rotor in the directionfrom F to G; it acts in the rotor of the motor pump MP in the directionfrom L to K, and the rotation of its rotor is obtained in direction Dequal to the direction C, of the rotor rotation of the impelling pump.

The debit variation of the impelling pump and the corresponding speedvariation of the motor pump, are going to be explained as follows:

to an increase in resistance, which opposes to the rotor rotation of themotor pump, there is the correspondence of an increase in the normalwork strength of the binary motor, which activates the rotor of theimpelling pump; to the increase in the said strength there is thecorrespondence of an increase in the fluid pressure, on the side HC 1 ofthe circuit of the hydrostatic transmission; by means of a hydrostaticextension HE, the said pressure increase is transmitted to the firstcylinder 6; the respective piston 4 impels the rod A, in order to reducethe amplitude of the decentralisation of the stator, so that the balancelevel of the said normal work strength of the binary motor may bere-established;

to a decrease of the said resistance, there is the correspondence of apressure decrease in the circuit HC 1, transmitted by the extension HEto the cylinder 6; the springs system 9 performs the piston retrocession4, and it is recovered the amplitude of the decentralisation of thestator referring to the anterior cycle;

in the impelling pump IP the amplitude of the decentralisation of thestator and the corresponding fluid debit, have a decreasing variation inrelation to the increasing variation of said resistance, which opposesto the rotation of the motor pump MP;

the rotation speed of the said motor pump, also has a decreasingvariation, in relation to the increasing variation of the saidresistance.

In FIG. 2, the motor pump MP has the rotation direction inverse to theone of the impelling pump IP;

the transmission command controls the activation of the vacuum effectthrough way V2 to the second cylinder 7, in order to impel the piston 5and the rod B, which is fastened to it in the inverse direction to theone of the rod A; it is obtained the decentralisation of the stator inthe direction of the rod B, inverse to the direction of the anteriordecentralisation;

in the impelling pump IP the fluid circulates in the direction from G toF and in the motor pump MP from K to L; the rotor rotation of the motorpump is in the direction E, inverse to the direction C of the rotorrotation of the impelling pump.

In FIG. 3, the motor pump has no rotation movement, though the rotationof the impelling pump is maintained;

the transmission command is not activated; the valve 8 is closed and novacuum effect is transmitted; the stator 2 of the impelling pump IP iscentralised and balanced by the action of the springs systems 10 and 11;

no fluid impulsion is transmitted, regardless of the speed rotation ofthe said impelling pump.

Several Applications

The control devices which were described with reference to theirapplication to a hydrostatic transmission, which includes a motor pump,may be also applied to other types of hydrostatic transmissions, forexample, replacing the motor pump by either static or linear movementhydrostatic devices.

The said devices may be also applied to a motor pump or simultaneouslyto an impelling pump and a motor pump.

The invention claimed is:
 1. A control device for a hydrostatictransmission, said transmission including a motor pump, in communicationwith an impelling pump by means of a fluid circuit, said impelling pumpcomprising a rotor and a stator contained inside a body; the fluid debitof said impelling pump is infinitely variable, in accordance with theinfinitely variable amplitude of the radial decentralization of saidstator, obtained by means of the impulsion of a first and second rod;the variable work pressures of the fluid which act in each internal sideof said stator are compensated and balanced on the correspondingexternal side, by equal fluid, thus resulting to be small andindependent from the said work pressures of the fluid, the needed forceapplied in the impulsion of said first and second rods; said controldevices of a hydrostatic transmission comprising: a first cylinder,which communicates with the side of the hydrostatic circuit by means ofthe hydrostatic extension; said first cylinder contains a first pistonwhich actuates on said first rod in order to obtain the infinitelyvariable decentralization of said stator; a second cylindercommunicating with a vacuum feeding circuit, by means of first andsecond ways; said first and second ways connected to a valve whichcommends the direction of actuation of the vacuum; said second cylindercontains a second piston fastened with said second rod, said second rodacting in order to obtain the variation of the direction of thecirculation of the fluid in said transmission; and first, second andthird spring systems, of laminar type, whose pressure control thereciprocating position of said first and second pistons and thereciprocating position of said first and second rods.
 2. The controldevice, according to claim 1, wherein the first piston of the firstcylinder impels the first rod through the top and its retrocession isobtained by means of the first spring system.
 3. The control devices,according to claim 1, wherein the second piston of the second cylinderis fastened with the second rod and its balance position is obtained bythe joint action of the second and third springs systems.
 4. The controldevices, according to claim 1, wherein the variable pressure obtained onthe side of the fluid circuit of the transmission, and produced by thevariable resistance which opposes rotation of the motor pump, istransmitted to the first cylinder by an extension of the said fluidcircuit.
 5. The control devices, according to claim 4, wherein saidvariable pressure transmitted to the first cylinder acts on the firstpiston; said first piston impels the first rod, in order to obtain adecreasing variation of the amplitude of the decentralization of thestator of the impelling pump, in correspondence with the increasingvariation of said pressure.
 6. The control devices, according to claim1, further comprising a transmission command formed by said valveinserted in a vacuum circuit with first and second ways, whichcommunicate with the second cylinder.
 7. The control devices, accordingto claim 6, wherein the regulation of the transmission command isperformed by said valve, directing through said first or second ways theactivation of the vacuum effect to the second cylinder, in order toobtain the impulsion of the second piston, and the decentralization ofthe stator, in the direction determined by the said command.
 8. Thecontrol devices of a hydrostatic transmission, according to claim 1,wherein: the transmission command drives the valve and directs theactivation of the vacuum effect in the direction of the first way, inorder to obtain the decentralization of the stator in the direction ofthe first rod; the rotation of the motor pump in the same rotationdirection of the impelling pump; the decreasing variation of therotation speed of said motor pump, in correspondence with the increasingvariation of the resistance which opposes to its rotation; said commanddrives the valve and directs the activation of the vacuum effect in thedirection of the second way, in order to obtain the decentralization ofthe stator in direction of the second rod, inverse to the one of thefirst rod; the rotation of the motor pump in the inverse direction tothe rotation of the impelling pump; said command closes the valve, doesnot activate the vacuum effect and achieves the centralization andbalance of the stator, by the joint action of the second and thirdsprings systems, in order to be not transmitted any impulsion fluid,regardless of the speed rotation of the impelling pump; the motor pumphas no rotation movement, though the rotation of the impelling ismaintained.
 9. The control devices of a hydrostatic transmission,according to claim 1, wherein the impelling pump or the motor pump, arestatic hydrostatic apparatus, or hydrostatic apparatus of linearmovement.
 10. The control devices of a hydrostatic transmission,according to claim 1, wherein being applied identically to a motor pump,or simultaneously to an impelling pump and a motor pump.
 11. Ahydrostatic transmission comprising: a hydrostatic pump; saidhydrostatic pump having a housing, a rotor, a stator about said rotor, afirst rod for decentralizing the stator in the housing, and a second rodfor decentralizing the stator in the housing; a motor pump, a fluidcircuit extending between said hydrostatic pump and said motor pump,said fluid circuit having a first branch and a second branch; a controldevice for controlling the transmission, said control device comprising:a first cylinder attached to said hydrostatic pump housing, a firstpiston in said first cylinder for moving said first rod, a fluidextension extending between said first cylinder and a branch of saidfluid circuit, a second cylinder attached to said hydrostatic pumphousing, a second piston in said second cylinder for moving said secondrod, a piston control device for causing movement of said first andsecond pistons, said piston control device having a valve connected tosaid second cylinder, said valve has a first port in communication withthe space between said second piston and said housing and a second portin communication with the space between said second piston and the topof the second cylinder.
 12. The hydrostatic transmission of claim 11,wherein said control device comprises: a fluid extension conduitextending between said second cylinder and a branch of said fluidcircuit.
 13. The hydrostatic transmission of claim 11, wherein saidfirst rod and said second rod are diametrically opposed.